#include<iostream>
using namespace std;
int main()
{
	int l, m,i=1,u,v;
	cin >> l >> m;
	int* p = new int[l];
	for (int i = 0; i < l; i++)
		p[i] = 1;
	while (i <= m)
	{
		cin >> u >> v;
		for (int j = u; j <= v; j++)
			if(p[j]!=0)
			p[j]--, l--;
		i++;
	}
	l += 1;
	cout << l ;
}